Travel Form

Longest... placeholder... ever...

Edit: HUZZAH! It's now a stag, as it was meant to be!

For all you "noobies," the default form of this spell for almost a decade was the crappy cheetah model that's now a minor glyph option. It's hard to believe I wrote this comment 5 years ago!

As of patch 7.1, the ground based travel form increases your speed by 100% when activated out of combat, and 40% when in combat or when in an arena or battleground. Previously it always increased speed by just 40%.

Which speed you get depends on your combat status when you shapeshift. So you keep the faster speed even if you enter combat, and will need to re-shift to upgrade your speed if you initially shifted while in combat.

The 100% speed increase is not affected by standard +speed items and effects, including Perfect Dreamgrove Blossom and Feline Swiftness. It's also not affected by guild perks and achievement rewards that increase mount speed.
Update: As of patch 7.2 travel form speed is affected by the +20% speed rewarded by Broken Isles Pathfinder Part One. It is still currently not affected by the guild perk Mount Up.

It is still affected by Sunblossom Pollen (sometimes grown in the fertile soil Druid class hall upgrade.) It's probably a bug, but using the pollen also allows other +speed effects to apply. I'm currently running around at 267% of normal run speed thanks to various +speed gear, significantly faster than a mounted player.
Update: Patch 7.1.5 changed the function of Sunblossom Pollen. It now reduces damage taken instead of increasing speed. It now has no effect on travel form.

Sometimes when I want to change to Travel Form quickly after walking from an inside place to an outside place, it took a few seconds to realize I was outside and it would finally cast. A trick I've found out is if you jump from an inside environment to an outside, the game realizes quicker that you've moved to an outside area. Probably when your feet land it refreshes it quicker. You can cast Travel Form instantly with this method. It's especially useful for BG's and you need a quick getaway if you have the WSG flag.